Some vehicles have two characteristics, among others. A first is that their ride height during normal operation is such that egress from and entrance to the vehicle is not as easy or convenient as it might be. Depending on the type of vehicle, the height could be lower or higher, to suit most people. With sports utility vehicles (SUVs) that have off road capabilities, the ride height of the vehicle, and thus of the passengers in the vehicle, is high, so that the vehicle has substantial ground clearance over rough terrain, as well as giving the driver and passengers a good viewing position to survey the ground being traversed. On the other hand, sports cars, or high performance cars frequently have a low ride height, because they will typically be driven only on good road surfaces and a low vehicle gives a low centre of gravity which improves vehicle handling, for example by reducing roll during cornering. A second characteristic of some vehicles is adjustable suspension for the vehicle, whereby the ride height can be adjusted. Typically, but not exclusively, such suspension systems are gas suspension systems (usually air, and referred to as such hereinafter) where ride height depends on the mass of air in the suspension system, which may be adjusted by operation of a pump (to increase pressure), or of a valve (to reduce pressure). The pressure is often in the region of 3 to 20 bar. Such air suspension may be provided in both SUVs and sports cars, although for different reasons. The higher the ride height of the vehicle, the more suspension travel the vehicle provides, although the comfort of the ride in the vehicle generally depends on their being the capability of suspension travel in both directions (i.e. up in the case of bumps being experienced or down in the case of holes). In both types of vehicle, the “normal” ride height for everyday situations may be a first height, whereas less usual situations may invoke a different, second ride height—higher in SUVs for off-road applications, and lower for sports cars when the driver wants to enter a sports driving mode. However, in SUV vehicles it may also be desirable to lower the suspension during extended road driving.
For an SUV, when it is in a raised suspension condition, or even in an intermediate position, passengers may be required to make a significant step up (for entrance into) or step down (for exit from) the vehicle, and conversely for a sports car or some performance cars.
It is known to lower vehicle suspension when a journey in a vehicle terminates and a driver (and any passenger(s)) is to leave the vehicle. An end-of-journey event is detected in the known systems and pressure is relieved from the suspension system when that occurs so that the vehicle sinks to its lowest suspension setting. However, an issue is that air suspension systems typically take a number of seconds (perhaps five or more) to evacuate completely and lower the vehicle to its rest height. Therefore the vehicle may still be in the process of lowering as a passenger egresses from the vehicle. This has some safety issues, as well as being disconcerting for passengers, who cannot then tell what height the ground is from their position if the vehicle is changing height while they are exiting.
It is an object of the present invention to provide a suspension system for a vehicle, and a vehicle incorporating such system, with improved end of journey arrangements, or at least to provide a system that addresses the above issues and mitigates some of the problems discussed.